The present invention relates to a display device and an electronic apparatus, and particularly to a flat-type (flat-panel-type) display device in which pixels each including an electro-optical element are arranged on rows and columns (in a matrix), and an electronic apparatus having the display device.
In recent years, in the field of display devices for image displaying, flat-type display devices in which pixels each including a light emitting element are arranged in a matrix are rapidly becoming widespread. As one of the flat-type display devices, e.g. an organic electro luminescence (EL) display device is developed and commercialization thereof is being advanced. The organic EL display device includes organic EL elements as the light emitting elements of the respective pixels. The organic EL element is a so-called current-driven electro-optical element whose light emission luminance varies depending on the value of the current that flows through the element, and is based on a phenomenon that light emission occurs in response to electric field application to an organic thin film.
The organic EL display device has the following features. Specifically, the organic EL display device has low power consumption because the organic EL element can be driven by application voltage equal to or lower than 10 V. Furthermore, the organic EL element is a self-luminous element. Therefore, the organic EL display device provides higher image visibility compared with a liquid crystal display device, which displays an image by controlling, for each pixel including a liquid crystal cell, the intensity of light from a light source (backlight) by using the liquid crystal cell. In addition, the organic EL display device does not need to have an illuminating unit such as a backlight, which is necessary for the liquid crystal display device, and thus is allowed to easily achieve reduced weight and thickness. Moreover, the response speed of the organic EL element is as very high as several microseconds, which causes no image lag in displaying of a moving image by the organic EL display device.
As the drive system for the organic EL display device, a simple- (passive-) matrix system or an active-matrix system can be employed, similarly to the liquid crystal display device. However, a display device of the simple-matrix system involves e.g. a problem that it is difficult to realize a large-size and high-definition display device because the light emission period of the electro-optical element becomes shorter as the number of scan lines increases, although the structure of the simple-matrix display device is simple.
Therefore, currently, a display device of the active-matrix system predominates, in which the current that flows through an electro-optical element is controlled by an active element, such as an insulated gate field effect transistor (typically, thin film transistor (TFT)), provided in a pixel circuit corresponding to this electro-optical element. In the display device of the active-matrix system, the electro-optical element continues light emission over the one-frame period. This easily realizes a display device having large size and high definition.
In general, the organic EL element used in the organic EL display device has a structure in which an organic layer composed of an organic material is interposed between a cathode electrode and an anode electrode in a sandwiched manner. For the light emission of the organic EL element, positive voltage is applied to the anode electrode and negative electrode is applied to the cathode electrode. Due to this voltage application, holes are injected into the organic layer from the anode electrode side and electrons are injected from the cathode electrode side. These holes and electrons recombine with each other inside the organic layer (light emitting layer), which causes the light emission.
The pixels as the minimum unit of image displaying by the organic EL display device (hereinafter, referred to as the “sub-pixels”) are so provided as to be separated for each of colors of red (R), green (G), and blue (B) as three primary colors of light. Each sub-pixel includes an organic EL element as an electro-optical element and a pixel contact for electrically connecting this organic EL element to a pixel circuit. The pixel circuit is a circuit to control the current that flows through the electro-optical element (organic EL element). Typically, the pixel circuit and the sub-pixel are provided with the one-to-one correspondence relationship.
It is effective that an active-matrix display device has a so-called top-face light extraction structure (hereinafter, referred to as the “top-emission structure”) for extracting light from the opposite side to a transparent insulating substrate on which the pixel circuits are formed, in order to assure a high aperture ratio of the organic EL element. In the organic EL display device of the top-emission structure, an upper electrode that sandwiches the organic layer together with a lower electrode is formed of e.g. a very thin metal film in order to assure high optical transmittance. Therefore, the sheet resistance of the upper electrode is high, and thus a voltage drop easily occurs when voltage is applied to the upper electrode.
To address this problem, a structure to prevent a voltage drop in the upper electrode has been proposed as a related art. In this structure, an auxiliary interconnect is formed at the same layer level as that of the lower electrode by using a low-resistance metal material (e.g. silver, aluminum), and the upper electrode is electrically connected to this auxiliary interconnect via an auxiliary interconnect contact (refer to e.g. Japanese Patent Laid-open No. 2004-207217).